Antiguided arrays have been optimized for single-spatial-mode operation to high output power. Diffraction-limited beam operation to cw power levels of 0.5 W have been reproducibly obtained. The high efficiency operation (wall plug efficiency = 20%) and demonstrated reliability make these practical devices, and useful for many applications requiring a high output power spatially coherent beam. Two-dimensional optical waveguide calculations demonstrate the mechanisms responsible for the high mode selectivity of these structures. It is also made clear why coupled-mode theory failed to predict how to obtain single-lobe phase-locked array operation, and what are the conditions to obtain stable, in-phase mode behavior.

Antiguide laser arrays have been fabricated and operated up to peak pulsed powers of 7.7 W in a beam with a full-width at half-maximum in the main lobe of 0.7°. Up to 0.7 W of continuous wave power is emitted into a radiation pattern 2.5 times the diffraction limit. By varying the temperature of the array to vary the operating wavelength of the device, the threshold gain condition of the array modes is altered, allowing thermal tuning of the far field of the device.

Twenty element resonant optical waveguide (ROW) antiguided arrays were locked to 2.6 times above the threshold level (2.6 x Ith) by injecting light from a master oscillator in a direction normal to the diode facet and only in one element of the array. The spectra and far-field output pattern of the SL were found to be independent of the MO beam position on the SL facet, and the far-field pattern was stable with wavelength detuning (i.e. no steering) . Single frequency tuning was achieved over a < 30 A spectral range, and the beam pattern was found to be stable and diffraction-limited for nearly resonant devices. Two and four coupled ROW arrays on a bar were also injection—locked by injecting an external MO into one element of one of the arrays. Two locked arrays were wavelength tuned over a 12 A spectral range.

Broad area traveling wave amplifiers in single-pass and double-pass configurations have been characterized using both analytical and experimental methods. Amplified emission up to 12.0 W in a nearly-diffraction-limited beam was achieved from double-pass amplifiers under short-pulse conditions, and 7.7 W in a nearly-diffraction-limited beam was achieved from single-pass amplifiers under long-pulse conditions.

The design and characteristics of active-grating surface emitting amplifiers are discussed. Performance projections indicate coherent power outputs of more than I W should be possible from devices that are 1 cm long. Preliminary experimental results on an AIGaAs/InGaAs active-grating MOPA are presented.

Ill this experimental study we investigate the guided mode-radiation mode coupling of periodic dielectric waveguides. The dispersion relation and the attenuation constant along the dielectric waveguide were measured around the second Bragg frequency. The far field radiation pattern was also measured. Floquet theorem was applied to solve wave equations. Zero order approximation was used in the design of waveguides. For surface emitting structures used in surface emitting lasers and couplers, the most important parameter is the dispersion relation and attenuation constant along the corrugated waveguide around the second Bragg frequency. The dispersion and attenuation measurement shows that the attenuation constant minimum occurs at the second Bragg frequency. This corresponds to the maximum Q point of the corrugated waveguide. Two side incidence shows that in the out of phase condition the radiation power is minimum at the second Bragg frequency and have two lobes.

A self-consistent thermal-electrical model of etched-well GaAs/A1GaAs doubleheterostructure VCSELs is used to optimize an individual device design with the goal of reducing the relative power loss due to heating and maximizing the optical output power. An optimal active-region diameter is determined, such that the excess of supplied power over the cw lasing threshold power at the corresponding active-region temperature is maximum. The role of other structural parameters, such as thicknesses and doping levels of both cladding layers, is also discussed. The single-emitter analysis is then modified to study very-large-size two-dimensional (2-D) VCSEL arrays. Severe crosstalk is predicted for closely packed arrays and conditions are identified for an array configuration that would not suffer from the excessive cross-talk penalty.

Monolithic in—plane surface emitting laser diode arrays with 45° micromirrors offer great promise for both coherent and incoherent applications. This paper describes several such laser diode structures in both the junction-up and junction-down configurations, and summarizes their design, fabrication and performance characteristics.

An InGaAs/GaAs vertical-cavity surface-emitting laser (VCSEL) with resonant periodic gain (RPG) was optically pumped using a pulsed dye laser at 760 nm with 500 ns pulse width. Output pulse energies at 918 nm in excess of 20 mJ were observed from a 3.3 mm diameter lasing spot. This corresponds to an efficiency of greater than 20%. Approximate area scaling of threshold and maximum available output power (limited by the optical pumping damage threshold) was demonstrated.

A rate-equation model of quantum-well lasers is presented which includes the effects of transport and partitioning of carriers between Ihe well and confinement layers. The predictions of this model are shown to be consistent with measurements of the structure-dependent reduction of the high-frequency response of these lasers. The implications of this model for the design of high-frequency quantum-well lasers is discussed. If their frequency response is not limited by electrical (AC) parasitics, or by heat generated at high power, the maximum modulation bandwidth of bulk semiconductor lasers is intrinsically limited to between about 25-45 GHz by damping due to nonlinear gain [1]. In addition to the limitations imposed by nonlinear gain, it has recently been shown [2] that the maximum modulation bandwidth of quantum-well lasers can under certain circumstances be severely reduced (< 1 0 GHz) by processes associated with their structure. The physical mechanisms responsible for these structure-dependent processes are the same as those which have been proposed to govern the gain recovery dynamics of quantum-well amplifiers [3]. In this paper, the "well-barrier hole burning" model [4] of quantum-well lasers is described. The results of measurements which are consistent with the model are presented. Finally, the implications of this model for the design of high-frequency quantum-well lasers are discussed.

A high-speed low-chirp 1.55 j.tm MQW-DFB laser is demonstrated through the optimization of an MQW active layer. A 3 dB bandwidth of 15 GHz and a record chirp width of 0.26 nm under 10 Gbit/s direct modulation were obtained. The dependence of the intrinsic dynamic properties, such as the relaxation oscillation frequency and damping K-factor, on the number of quantum wells is also investigated. The physical origin of the nonlinear damping is investigated by focusing on the laser structure and the wavelength dependence of the nonlinear gain coefficient e in semiconductor lasers.

The differential gain, modulation response, and damping rate of strained-layer Ino•3Ga(J•7As multiple quantum well (MQW) short cavity graded-index separate confmement heterostrucutre (GRINSCH) and SCH lasers fabricated by chemically-assisted ion beam etching (CAIBE) are analyzed. Calculated differential gains vary from 0.7 to. 1 .6 x 1015 cm2, with only relatively long lasers of 400 p.m demonstrating very high differential gain. For the GRINSCH lasers, a CW 3-dB bandwidth of 22 GHz has been measured that is limited primarily by heating and a low frequency rolloff. The latter is improved dramatically using an SCH design resulting in an improvement of the 3-dB bandwidth to 28 GHz. Cather transport theory (also known as well-barrier hole burning) is shown to model the damping behavior of quantum well lasers from low to moderate photon densities.

High-power laser diodes operating in the wavelength range of 640 to 675 nm are described. Using a strained-layer, single quantum well, epitaxial structure in conjunction with oxide-stripe construction, CW power outputs of individual diodes in excess of 1 watt at 670 nm and over 450 mW at 640 nm have been achieved. These accomplishments were made possible by reducing the room temperature CW threshold current density to slightly over 300 A/sq cm at 670 nm and 560 A/sq cm at 640 nm. Measurements have also been made of spectral output, characteristic temperature, far-field intensity, operating lifetime, and internal laser parameters.

We report recent results in high power visible diode lasers operating in both the 680 nm band and the 630 nm band. Continuous wave (CW) output powers in excess of 1 W from a 100 p.m aperture and 8.5Wfrom a monolithic 8 mm bar have been obtained in the 680 nm band. At 633 nm, 900 mW have been measured from a 100 jim wide aperture and 3 W from a 1 cm bar. We also discuss the temperature and length dependence of the threshold current density and external efficiency.

The fabrication and characteristics of the first Hg(1-x)Cd(x)Te double heterostructure mid-IR injection laser (Zandian et al., 1991) are described in detail, and new results on an expanded range of operation of this laser are presented. Three new double heterostructures were grown, which all produced working lasers operating under pulsed current at temperatures between 40 and 90 K. At 77 K, their emission wavelengths were 2.9, 3.4, and 3.9 microns; the lowest threshold current density measured was 521 A/sq cm, very close to that predicted by a numerical calculation.

We have observed laser action in InO7GaO3AsO72SbO28 IInPO.7SbO.3 double heterojunction, diode lasers at ? = 3.06 .tm. The maximum operating temperature was 35 K. The threshold current densities were in the range of 200 - 330 A /cm These devices were grown by organometallic vapor-phase epitaxy.

Degradation modes and reliability in various types of semiconductor lasers are reviewed in connection with the system application. Reliability and marked degradation modes of conventional DH type Fabry-Perot (FP) and distributed feedback (DFB)lasers are first clarified. Based on their degradation modes,new devices, such as highly coherent multiple-quantum-well (MQW)lasers and strained (M)QW lasers including pumping sources of Er3-doped fiber amplifier, are discussed from the viewpoint of the degradation modes and reliability.

Results are presented on catastrophic damage limits and life-test measurements for four types of high-power laser diodes operating at wavelengths between 980 nm and 690 nm. The laser diodes under consideration are CW multimode lasers, CW laser bars, quasi-CW bars/2D stacked arrays, and single transverse mode lasers.

The facet heating behavior of A1GaAs ridge-waveguided single quantum well (SQW) lasers and doubleheterojunction (DH) lasers was measured using Raman microprobe spectroscopy. For the SQW lasers, samples with various ridge widths and cavity lengths were measured as a function of output power and injection current. The facet temperature was found to scale with the injection current density rather than the photon flux. In addition, no large discontinuities were found below and above the lasmg threshold suggesting that the absorption of the emitted photons plays only a minor role in the initial stage of SQW facet heating. In contrast, a clear discontinuity in the facet temperature rise was found below and above the lasing threshold for the DH lasers indicating a substantial contribution to facet heating by the photon flux. The data suggest a large difference in the facet absorption of the lasing photons between the two types of lasers. This is further supported by the effect of argon laser probe beam induced facet heating on the diode laser's output power.

The paper discusses the characteristics of single-stripe AlGaAs high-power lasers with a novel window structure, named the 'window grown on facets (WGF)'(Sasaki et al., 1991), in which window layers are epitaxially grown on cleaved (110) facets, independent of the internal laser structure. The WGF technique was applied to the V-channeled substrate inner stripe (VSIS) lasers in the wavelength range 780-830 nm. Excellent high-power and high-reliability characteristics of the VSIS lasers with WGF structure were demonstrated. Results of reliability obtained at 100 mW (830 nm) and at 70 mW (at 780 nm) are considered of significance for the development of communications, SHG, and optical storage memory systems.

The use of high power laser diodes in applications such as pumping of solid state lasers requires devices which are highly reliable. We report the results of a series of experiments in which the effects on device reliability of several key processing steps are investigated. Electron Beam Induced Current (EBIC) is used to nondestructively characterize the Dark Line Defects (DLD5) throughout the lifetest and provides information regarding the source and propagation of the DLDs.

The current status and understanding of various degradation phenomena in III-V optoelectronic devices are discussed, with special consideration given to semiconductor lasers and light emitting diodes fabricated from GaAlAs/GaAs, InGaAsP/InP, and InGaAsP/InGaP/GaAd double-heterostructure materials. Three major degradation phenomena are discussed: rapid degradation, gradual degradation, and catastrophic failure. For each type of these degradation phenomena, methods for eliminating degradation are proposed.

Research into new material systems to both extend the operating wavelength and improve the performance of the GaAs/AlGaAs material system has led to several insights into the reliability of wide bandgap (E(g) greater than 1eV) semiconductor lasers. Strained InGaAs lasers, operating in the wavelength range 0.9-1.1 micron, have eliminated sudden failures and exhibited very low gradual degradation rates. Strained InAlGaAs lasers, a possible replacement for AlGaAs lasers at 0.8 micron have shown the potential to both eliminate sudden failures and improve gradual degradation as compared to AlGaAs lasers. Finally, visible GaInP lasers, operating at 0.65 micron, have eliminated sudden failures and exhibited surprising gradual degradation characteristics for lasers operating at modest efficiencies. Specific results and subsequent conclusions with the supporting life test characteristics and failure analysis are contained in this work.

Picosecond pulse amplification in modulated amplifiers is demonstrated with negligible pulse distortion for modulation frequencies between 1 and 4 0Hz. Existing measurements show that up to 2.5 GHz modulation can be achieved with a gate "on" time of 200 ps. A numerical model is reported which simulates the behaviour of diode laser amplifiers under RF current modulation and is shown to be in good agreementwith experimental demonstration. A simple analytical modelis also reported to indicate the physical causes in observed operating trends. It is shown that in optimized bulk devices, good modulation depth could potentially be achieved with a 100 ps gate "on" time at 5GHz modulation frequency.

We designed a new all-MOVPE low-RC BH laser structure with semi-insulating (SI) InPlayers. This structure was designed to avoid a selective epitaxy step. The fabrication process consists of three MOVPE steps. An extremely low capacitance below 0.6 pP and the series resistance around 3 (RC product < 2 ps) of the laser structure was observed. Using this new structure a 1 .3 jtm bulk laser had a nicely smooth optical response with bandwidth in a large excess of 18GHz (our measurement limit). A fitting procedure, using the laser response transfer function, confirmed an neglecting RC product (2 ps), a power limited bandwidth of about 21 GHz and excellent RF modulation efficiency.

A wavelength tunable 4-element laser array is fabricated with high performances suitable for the frequency division multiplexing (FDM) system. The array consists of four 1 .55 j.m DFB(distributed feedback) PPIBH (p-substrate partially inverted buried heterostructure) lasers with beam spacing of 125 jim. The lasing wavelength is tuned by changing the ratio of input currents to the two electrodes. The lasing frequency of the array can be allocated with a frequency interval of 10 GHz. An FM efficiency as large as 1 GHz/mA and a flat FM response with variation less than 3 dB in the modulation frequency range from 20 kHz to 1 GHz have been realized. An electrical crosstalk is less than -30 dB up to 800 MHz.

The design, fabrication, and characteristics of high power 980 nm strained layer lasers will be described in detail. These lnGaAs/GaAs ridge waveguide lasers show excellent optical beam quality with total fundamental mode powers of approximately 200 mW. Cavity losses are less than 3 cm¹ , and internal efficiencies approach 1 00%. Single frequency operation is typically observed for these lasers, and side mode suppression ratios of 30 dB and linewidths of 2 MHz are common.

Highpower single mode InGaAs lasers for emitting at 980mn have been developed. Life test data and failure analysis results are discussed. Coupling efficiency into single mode fiber as a function of beam ellipticity is also studied.

We describe 2.5Mm wide Ridge Waveguide Lasers emitting in the wavelength range 1045nm-1065nm. These are fabricated from strained layer single quantum well epitaxial heterostructures with 30%-31% InAs in the quantum well. The devices exhibit stable single spatial mode, single spectral line operation over a wide range of output power and temperature. Preliminary data suggests that reliable high power CW operation may be obtained.

This paper describes semiconductor laser arrays placed in an external Talbot cavity. The external Talbot cavity couples the light between many adjacent lasers such that all lasers operate at the same frequency and phase, resulting in a high power diffraction limited output beam. We designed a compact cavity which is comprised of a 30 by 50 element monolithic 2-D laser array, a GaP mass transport lens array, a liquid crystal array, a phase sensing and control system and a waveguide. Initial results obtained from a 20 element linear Ta1bOt cavity with a calculated mode discrimination similar to the 2-D cavity demonstrate in excess of 30 mW cw per laser element in a diffraction limited far field. In addition we have also demonstrated 50 Watt CW incoherent output power from a monolithic 2D laser array

A method was developed for sensing the phases of a two-dimensional array of coherent sources. The method is based upon phase contrast imaging and was developed to correct the phases of individual GaAlAs emitters in a two-dimensional external cavity laser array. This paper describes the method and presents results for an 18-element linear Talbot laser cavity and for an experimentally simulated 12 x 12 array. Phase correction was achieved using a nematic liquid crystal array.

The frequency locking range of a laser diode array was experimentally determined. A one-dimensional array of seven lasers was phase-locked by placing it in an external optical cavity to establish coupling between the lasers. It was found that the experimental frequency locking range was four times greater than the theoretical locking range. The large experimental locking range demonstrates that there appears to be a greater tolerance of path-length errors in phase-locked laser arrays than the theory had earlier implied.

An approach to mass-production of triple quantum well lasers with a buried-ridge, loss-guided inner-stripe structure is demonstrated, using a large-scale metalorganic chemical vapor deposition. The lasers obtained from nine epi-wafers grown at one time show the uniform characteristics. In regard to high-power characteristics, the fundamental transverse mode up to 100mW and the maximum output power of - 170mW are realized at room temperature. Even at 95 C, the light output power of 100mW is obtained. The lasers have been operating over 1000 hours without failure at 6O C, 50mW. To realize the further uniformity and reproducibility of the laser characteristics, we have Introduced a newly developed etching method with an etching stop layer in the ridge formation.

Single-mode strained-layer lasers have been fabricated which use buried second-order gratings for distributed Bragg reflectors. The lasers contain a strained GaInAs quantum well in the active region and operate in an edge emitting fashion with CW powers in excess of 110 mW. Single longitudinal and transverse mode operation is maintained at about 971.9 nm up to 42 mW. Total power conversion efficiencies as high as 28 percent have been observed. The longitudinal and transverse mode behavior is stable under 90 percent amplitude modulation with 50 percent duty cycle pulses at 10 kHz and 10 MHz. Preliminary life-test data at 40 C also indicate room temperature lifetimes in excess of 45,000 hours.

A highly reliable, 150 mW high-power semiconductor laser that oscillates at a wavelength of 860 nm has been developed. This device has a 0.7 jim thick p-cladding layer, a 900 jim long cavity length, and current-blocking regions near the cavity facets for high output power and high reliability. Stable, fundamental transverse mode and single longitudinal mode operation were obtained up to 230 mW, and the maximum output power was 350 mW under CW operation. Stable operation under 150 mW at 50°C was confirmed for more than 2000 hrs.

While considerable attention has rightly been paid to the spatial coherence properties of high-power semiconductor lasers, very little work has been done to optimize their temporal coherence, as might be required by applications such as pulsed-Doppler laser radar, widespread optical clock distribution in dispersive channels, and spectroscopy. Here we describe the operation of a wide stripe GRIN-SCH-SQW laser in external cavities. A high-reflectivity coating ( R - 85 %) was deposited on one side and a anti-reflection coating (R < 1%) was deposited on the other (internal) facet. A simple mirror external cavity gave maximum threshold reduction (to the original threshold current) but the longitudinal mode spectrum was broad and unstable. By contrast, when a diffraction grating was used as the external reflector, the laser operated up to at least 2.5 'th in a single, < 0.5 A, instrument limited longitudinal mode which was tunable over more than 300 A. Using this configuration the laser produced more than 500 mW in pulsed mode. The output wavelength was extremely stable with respect to variations in current and temperature.

A millisecond-pulse-length 5-bar 2D diode laser array was fabricated and operated, demonstrating 1-msec pulse widths at 40 Hz. Peak output power was 250 W at a conversion efficiency of 36 percent. The wavelength spectrum integrated over the current pulse exhibited shifts to longer wavelengths and broadening on the order of 1 nm as the pulse width was increased from 0.2 msec to 1 msec at constant duty factor.

High-power large-optical-cavity (LOC) InGaAsP-InP lasers emitting at 1.55 micron were prepared by using a proper LPE growth technique. Long-lived LOC lasers with the output power higher than 2 W in pulsed operation at room temperature were fabricated, with the threshold currents as low as Jth = 2.7 KA/sq cm or less and temperature stability as high as T0 of 130 K.

Semiconducft lasers which can produce high output jxwer in a single fundamental lateral mode have in recent years become a topic of signifxant research pj ss frr maximum energy transf& when coupling the laser output to other optical components h as waveguide, optical fibers, or beam forming optics Many applications, such as free-spe commuthcation, highSpCCd optical printing, and biomedical laser technology, could greatly benefit from advances in high power, single mo& laser thos Attempts at producing fundamental mode operation from varus types of laser arrays have met with only limited success. Wide stripe miconductcr lasers can produce high 1x,w& (-8 W), and require only the most basic fabricatiou steps. However, stripe widths of more than 1-2 μn produce multiple transverse m spectra and filamentation due to carrierinduced index variations. Filamentaüon can degrade the farfie1d psofile and cause angular beam steering at high ouqit power. Using an anti-reflection coated wide stripe laser within a simple external cavity, we have produced both high output power and fundamental moik operation in the lateral dimension by filtering out higher order modes in pulsed operation. Mode discrimination is realized using an unstable cavity in the lateral dimension. The unstable cavity was fonned using a cylindrical lens within the external cavity which causes the higher order mxies to be more kssy than the fundamental. A simple Gaussian beam wopagaon model was used to xedict the effts of cylindrical lens pIzement within the external cavity. With this inokl we were able to calculate an overlap integral, or modal coupling term for each transverse mode. In our model the coupling term was considered to be spatially independent and was used to estimate the effective reflectivity of the external cavity system. Ung the cakulated effective reflectivity the threshold gath requirement for ch of the higher order modes was calculated , in order to predict the optimum placement of the cylindrical lens. Threshold gain was plotted as a fimction of the effective reflectivity (mxJal overlap) in order to predict the optimum placement of the cylindrical lens. In experiment, a 100 μm wide stripe laser was coupled to the anamorphic external cavity. WIth this cocfiguration, we achieved a nearly diffraction-limited beam at greater than 250 mW; this reprents a ftcr of ten improvement over the external cavity without the cylindrical lens. Beam quality was maintained to 3 times the original (uncoated) threshold injection current with negligible steering effects.

Deep level transient spectroscopy (DLTS) of deep levels occurring at MOCVD grown and regrown interfaces is described as a function of surface preparation. We examine two types of interfaces: 1 ) nGaAs grown on SI-GaAs and 2) A10,1Ga0,9As regrowth on Alo.lGao,9As. Surface preparation includes both shallow and deep wet etching, passivation with (NH)2S, and in-situ heat treatments and HCL etching. A new electron trap with EcEa 0.1 1 eV and 1019 cm2 and a new minority carrier trap with Ea E 0.18 eV and 10-15 cm2 were found in GaAs samples. The minority carrier trap is related to sulphur passivation. Four traps were found in the AlGai..As regrown samples. It is demonstrated that (NH)2S passivation before MOCVD improves interface quality for both the GaAs and Al1Ga0,9As grown and regrown layers.

It is presented the principle of operation and some experimental results reached with one developed device composed of a couple of fiber bundles and a simple diode laser and photodetector. This device is applied for contactiess displacement measurements on a range of 3.500 to 6.500mm and with +1— 017. of accuracy.

Fabrication and lasing characteristics of prototype MOCVD-grown GaAs/AlGaAs/AlAs distributed-feedback resonant-periodic-gain surface-emitting lasers are reported. The new structure eliminates the need for end reflectors in earlier resonant-periodic-gain lasers, thereby reducing considerably the total thickness of the device. A new hybrid distributed-Bragg-reflector/distributed-feedback resonant-periodic-gain structure, compatible with the transverse-junction electrical pumping scheme, is also proposed.

Common methods for frequency stabilizing diode lasers systems employ gratings, etalons, optical electric double feedback, atomic resonance and a Faraday cell with low magnetic field. Our method, the Faraday Anomalous Dispersion Optical Transmitter (FADOT) laser locking, is much simpler than other schemes. The FADO'r commercial laser diodes with no antireflection coatings, an atomic Faraday cell with a single polarizer, and an output coupler to form a compound cavity. This method is vibration insensitive, thermal expansion effects are minimal, and the system has a frequency pull in range of 443.2 GHz (9A). Our technique is based on the Faraday Anomalous Dispersion Optical Filter. This method has potential applications in optical communication, remote sensing, and pumping laser excited optical filters. We present the first theoretical model for the FADOT and compare the calculations to our experimental results.

No abstract available

We report the improved LPE regrowth prooess o InGaAsP/InP BR lasers.This method is based on the efeot o laP layers growth seleotivity. The proposed etched mesa proi1e provides the localization o! blocking p-n-junction on the mesa sidewall in the close vicinity o active layer. The mechanism responsible ror the increase of threshold current density(Jth) and the decrease o differential quantum eicienoy (ηd) in narrow (W<1Oμm) BR lasers was revealed in the set or special experiments. The modification of the rerowth process allowed to improve the lasing characteristics and to achieve 160 mW single-lobe output.

Free carrier effects in a modulation-doped GaAs QW placed in the n-region of a p-n junction were successfully used to obtain active Q-switching in a two-section GaAs/AIGaAs DH laser structure. The modulator-section uses the blue shift of the QW absorption edge due to band filling by a 2D electron gas which concentration could be controlled between 0 and 8 x 1011 cm2 by external bias voltage. Only about 100 mV of the modulating voltage was necessary to provide stable active Q-switching. The threshold injection current density ranged from 400 to 800 A/cm2 .The modulation bandwidth estimated to be not less than 4 -5 GHz. A simple electrostatic model is suggested to describe electrooptical phenomena in a modulation-doped QW which underlie the operation of the device.

It is shown that in homogeneous GaAs surface emitting cavity the laser efficiency may be high enough owing to the cavity passive part bleaching, induced by optical field in the laser cavity. The external differential efficiency of 19 and 5.7 % , obtained at 77 and 300 K, respectively, are limited only by a free carrier absorption both in active and passive parts of the cavity. The further laser efficiency improvement is obtained in the variable-gap GaA1As heterostructure,in which the narrow-gap side is used as the cavity active part. The room temperature laser emission of S watts power and external differential efficiency of 14% have been obtained in the GaA1As with grad Eg 3-4 eV/mm under electron beam of 0.6 mA current at the electron energy of 75keV.

InGaAs/GaAs strained-layer quantum well lasers have been successfully demonstrated for very high temperature CW operation up to 200 C. The lasers show promising reliability data at 70 C, 100 C, and 125 C and high output power of about 300 mW with a 3-micron ridge-waveguide structure.

Aluminum-free In_O.2Ga_0.8As/GaAs/In_0.49Ga_0.5l P strained-layer-quantum-well lasers are grown by gas-source molecular beam epitaxy (GSMBE) for the first time. Ridge waveguide lasers of 3 p.m width show 1.0 im lasing wavelength at room temperature under continuous wave (CW) conditions and have low threshold currents (7 mA and 12 mA for 254 p.m and 508 jim-long cavity, respectively), high external quantum efficiencies (0.9 mW/mA), and high peak powers (160 mW). High temperature CW operation has been demonstrated up to 185°C, which is comparable to the best result (200°C) reported for the InGaAs/GaAs/AlGaAs lasers. Self-align index guided InGaAs/GaAsIInGaP lasers are also fabricated using GSMBE in two growth steps. Threshold current of 12 mA with an external differential quantum efficiency of 0.68 mW/mA is obtained from a 2.5 jtm x 508 tm self-aligned laser at room temperature under CW operation condition.

We report the fabrication and performance of (InAs)1 /(GaAs)4 short-period superlattices (SPS) strained quantum-well lasers emiuing near 1 jim. The (InAs)1 /(GaAs)4 superlattices is an ordered counterpart of 'NO.2Ga8As random alloy, and provides an alternative method of fabricating high speed electronic and photonic devices. The 0.96-mm-long devices have lased with a broad area threshold current density of 100 A cm 2 The 250-p.m long ridge waveguide lasers fabricated on the same wafer have a threshold current of 10 mA, an external differential quantum efficiency of 0.35 mW/mA/facet and have operated to a temperature of 200°C with a characteristic temperature T0 = l75K in the 2O°C to 8O°C range.

The effect of high temperature on the threshold gain and threshold current density of an InGaAs (GaAs based) strained quantum well laser is examined both theoretically and experimentally. It is shown that designing a quantum well laser for low threshold gain through the use of a long laser cavity and/or high reflectivity facet coatings will reduce the temperature induced threshold current increase. This result is related to the nonlinear dependence of quantum well gain and current density on carrier density. The high temperature characteristics of strained InGaAs and GaAs QWs are also compared.

No abstract available

We have successfully used low-pressure metal-organic chemical vapor deposition (LP-MOCVD) to grow GaAs/A1GaAs vertical-cavity surface-emitting lasers containing graded-index distributed Bragg reflector (DBR) mirrors. The continuously-graded mirror heterojunctions were obtained by maintaining a constant growth temperature while ramping the reactant gas flows. Graded interfaces were found to reduce the energy-band discontinuities, resulting in improved electrical charteristics. A 35 p.m diameter device has a series resistance of 22 , a CW output power of 2 mW, a threshold current density of 1.2 kA/cm₂, an overall power efficiency of 3.0%, and a turn-on voltage of 2.3 V.

We have obtained high power single-lateral-mode operation in wide-stripe InGaAs/GaAs/A1GaAs semiconductor lasers using a monolithic unstable resonator (consisting of diverging elements incorporated above an asymmetric GRIN-SCH). The fabrication involves MOCVD regrowth after wet-chemical etching of lens-like patterns in a GaAs layer above the active region. Pulsed output powers of 175 mW and 490 mW have been obtained in 170 p.m and 100 tm wide lasers respectively, with spatial coherence in the near-field exceeding 60%. We observe good lateral mode discrimination upto 3.5 times threshold in 100 .tm stripes with a round-trip magnification of 6.4.

We have developed a method to etch Ill-V semiconductor materials to produce a parabolic cross sectioned channel. Laser-assisted wet-chemical etching has been used to produce channels 20 to 200 p.m wide, with a corresponding center depth of 0.1 to 0.5 .tm. We will discuss recent experimental results of etching n-type gallium arsenide (GaAs). Future considerations include the fabrication of antiguided wide-stripe laser diodes using this procedure.

We report on novel laterally-injected lasers by impurity-induced disordering (lID) having a self-aligned structure and planar configuration. The laterally-injected lID (LID) lasers have minimum threshold current I=2.6 mA, maximum light output 12 mW with differential quantum efficiency 1d3697' per facet at RT CW operation. The LID laser can also be injected vertically by using an ndoped (instead of semi-insulating) GaAs substrate and making additional ohmic contact on the bottom surface of the wafer. The problem of having much higher series resistance when the laser was in the lateral injection mode than in the vertical injection mode was investigated by studying the I-V characteristics of different combinations of the top and bottom ohmic contacts, and was solved by revising the material design and the device processing procedures.

Ar⁺ ion milling of A1_xGa_1-xAs layers grown by Low Pressure MOCVD, with aluminum compositions from 10 to 80% and for ion energies from 300to 1200 eV is reported in this work. The etch rate decreases with Al composition and increases with ion energy. The ion milling rate was found to depend exponentially on the ion energy, with an activation energy of 0.02 eV. Results are compared with the milling of a GaAs control sample and device layers etched under similar conditions. Etching was also studied as a function of ion angle-of-incidence.

Although optoelectronic components are used widely in the telecommunications industry, this technology has barely touched the potential of what could be vast markets in broadband local loop and computer interconnection applications. The reliability, performance and particularly the cost of optoelectronic components must be improved for these applications to develop. Issues involving component packaging to a large extent determine the level to which these application criteria are met.1 This paper explores advances in semiconductor laser packaging that are aimed at reaching levels of component integration required for extensive use of optoelectronics in computer and communications systems applications.

Detailed performance results and fabrication techniques for an efficient and low thermal impedance laser diode array heatsink are presented. High duty factor or even CW operation of fully filled laser diode arrays is enabled at high average power. Low thermal impedance is achieved using a liquid coolant and laminar flow through microchannels. The microchannels are fabricated in silicon using a photolithographic pattern definition procedure followed by anisotropic chemical etching. A modular rack-and-stack architecture is adopted for the heatsink design allowing arbitrarily large two-dimensional arrays to be fabricated and easily maintained. The excellent thermal control of the microchannel cooled heatsinks is ideally suited to pump array requirements for high average power crystalline lasers because of the stringent temperature demands that result from coupling the diode light to several nanometers wide absorption features characteristic of lasing ions in crystals.

A significant challenge for achieving higher average power two-dimensional diode lasers lies in effectively removing the enormous heat flux generated by these devices. Packaging based on microchannel cooling offers a practical means of addressing the thermal management problem. Microchannel coolers are capable of extracting high heat fluxes ( > 60 Watts/cm²) while maintaining a highly uniform surface temperature. These coolers require less than 0.5 1pm coolant flow and operate with nearly constant thermal impedance over a range of 10 to 50 psig fluid pressure. State-of the -art performance of two-dimensional arrays mounted on microchannel plates confirm the thermal characteristics of the coolers. The thermal impedance of the entire package (cooling fluid to diode junction) is less than 0.33 °C.cm²/W. Arrays exceeding 1500 W peak power at duty cycle of 2% routinely exhibit less than 4 nm bandwidth with accurate control of center wavelength.

Axial strain may be determined by monitoring the phase shift of modes of a variety of optical fiber sensors. In this paper, the exact solution of a circular optical fiber is used to calculate the phase shift of the TE and TM modes. Whenever an optical fiber is stressed, the optical path length, the index of refraction, and the propagation constants of each fiber mode change. In consequence, the modal phase term, beta(ln)z, of the fields is shifted by an amount Delta phi. In certain cases, it is desirable to control the phase shift term in order to make the fiber either more or less sensitive to certain kinds of strain. It is shown that it can be accomplished by choosing appropriate fiber parameters.

The paper describes the design of high-performance vertical-cavity surface-emitting lasers (VCSELs) with a low series resistance, low threshold voltage and power dissipation, and high differential quantum efficiency. The integration of these VCSELs with heterojunction phototransistors and photothyristors yielded a new family of high-performance optical switches that can perform switching, logic, regeneration, and memory functions. Moreover, the switches are cascadable and functionally integrable.

We report stabilization of self-pulsating laser diodes using a combination of self-injection locking and frequency locked loops. Short term frequency stability better than 1 part in 106 (3ffl linewidth <1 kHz at 1 .3 GHz) was readily achieved with continuous tunability from 600 MHz to over 3 GHz using inexpensive commercial devices. Experimental results illustrating the effects of loop operation on error performance in subcarrier multiplexed (SCM) systems are presented.

The background theory of backscatter modulation and velocimetry using laser diodes is presented together with an experimental demonstration of the application of these laser diodes in laser Doppler velocimetry (LDV). The sensitivity of the laser diode system to backscatter from a diffusely reflecting target is greater than -60 dB. Tests of an LDV system using a moving air mass as the target are described. Possible applications of these systems include airspeed measurements, collision avoidance, and tracking distant objects.

A system was developed which is capable of measuring the time-resolved far-field radiation patterns from a high-power semiconductor laser under intensity modulated conditions. Angular steering of the fundamental spatial mode was observed, with pointing variations as large as 0.5 deg, or 7.5 percent of the beamwidth, during the time of the optical pulse. The variations in pointing angle were directly related to gradients in the transverse index profile of the laser, which may oscillate based on lateral spatial hole burning of the gain and carrier density.